This invention relates generally to Magneto-Rheological (MR) devices and more particularly to an improved design for an MR damping element.
Devices for suspending parts and controlling or damping their movement relative to one another, are known in the art. For example, such devices are known and used in the automotive field in vehicle suspension systems. The devices might take the form of shocks, struts and other motion or vibration damping structures.
Generally, many of those devices utilize fluids for controlling the relative movement of the mechanical parts. For example, hydraulic fluid may be utilized as a medium for creating damping forces or torques or controlling motion, shock and vibrations. One class of such movement control devices utilizes a fluid medium which is controllable through the use of magnetic fields. Such magnetically controlled fluid is referred to as magneto-rheological, or MR, fluid and is comprised of small, soft magnetic particles dispersed within a liquid carrier. The particles are often generally round and suitable liquid carrier fluids include hydraulic oils and the like. MR fluids exhibit a thickening behavior (a rheology change), often referred to as xe2x80x9capparent viscosity change,xe2x80x9d upon being exposed to magnetic fields of sufficient strength. The higher the magnetic field strength to which the MR fluid is exposed, the higher the flow restriction or damping force that can be achieved in the MR device, and vice versa. That is, the flow properties of MR fluids may be selectively altered by magnetic fields.
A typical MR device, for example, utilizes an iron core structure disposed within a metal cylinder or casing which is filled with the MR fluid. The MR fluid flows through a restricted passage or gap within the cylinder or casing or within the core structure itself. The passage, or gap, is magnetically controlled to control the characteristics of the flow of the controllable MR fluid therethrough. To that end, a magnetic field generator, such as a wire coil wound around the core structure, varies the magnetic field in the core and in the fluid passage by variation of electrical current through the coil. The selectively variable magnetic field dictates the characteristics of the fluid in the restricted passage. The relative movement of the parts is then regulated by controlling the characteristics of the fluid.
Existing designs of such MR devices use one or more coils wound in a groove around the outside of the core. However, such designs have certain drawbacks. For example, the damping effects associated with such a design may not be sufficient or desirable for the particular application of the MR device.
Furthermore, such designs utilize core structures and magnetic field generators which may sometimes be difficult and expensive to construct and manufacture.
Still further, the construction of the core structure may sometimes limit its ultimate packaging and the particular uses for such a core.
Therefore, it is an objective of the present invention to improve the performance of MR devices. It is further an objective to do so by improving the core. It is another objective to simplify and enhance the fabrication and manufacturing of such devices and the core elements in such a device. It is still another objective to provide alternative manufacturing and packaging options for the MR devices. These and other objectives will become more readily apparent from the description of the invention below.
The Magneto-Rheological (MR) damping device of this application addresses the above objectives and utilizes a unique construction for improved performance and enhanced fabrication and manufacturing.
Specifically, the MR damping device comprises a core element capable of acting as a magnetic circuit which carries a magnetic flux. The core element is surrounded by a case element and a passage exists between the case element and the core element. Generally, the size and shape of the case element, which may be in the shape of a cylinder or ring, defines the size and shape of the passage. An amount of MR fluid is positioned between the core element and case element to flow within the passage. A magnetic flux generator is positioned adjacent a portion of the core element and is operable for generating a magnetic flux which acts upon the MR fluid in the passage to affect the flow of fluid in the passage.
In accordance with one aspect of the present invention, the core element has a unique design comprising a plurality of stacked, generally flat laminations which, when stacked, collectively form the core element. The laminations form a series of individual magnetic poles with gaps therebetween, and the magnetic flux generator is operable to generate a magnetic flux in the poles and case element and across the gaps to affect the fluid flow in the passage.
More specifically, the laminations are shaped so that collectively they form a core element comprising a series of arms which project radially from a center axis of the core. The arms form the magnetic poles, and adjacent arms are oppositely magnetically polarized. In that way, the flux is located between adjacent arms and in the case element, and in that way, the magnetic flux extends across the passage and over the gap. Each arm includes an annular head, and the length of the head defines the size of the gap between the alternating magnetic poles. The size and shape of the annular heads of each arm might be adjusted to adjust the gap and thereby adjust the effect which the core element has on the MR fluid.
To form the magnetic flux generator, one embodiment of the invention utilizes electrically conductive coils which are wound around the radially projecting arms. An individual coil is wound around each arm. In order to oppositely polarize adjacent arms, electrical current is directed through the adjacent coils in opposite directions to define the opposite magnetic poles in the adjacent arms. A plastic housing is utilized to encase the core element and magnetic flux generator. The housing leaves the annular heads of the radial arms exposed for direction of the magnetic flux between the core element and the case element and across the passage therebetween. The MR fluid moving between the case element and the core element may thereby be affected by the magnetic fields generated in the passage by the arms of the core element. In one particular use of the invention, the device is used for vehicle suspensions, such as in shock absorbers and struts. However, it may have other uses as well.
With respect to one possible embodiment, the case element includes a fluid inlet and a fluid outlet, and the case element contains the MR fluid which flows between the core element and the case element. By magnetically affecting that fluid flow, the movement of fluid through the inlet and outlet of the damping device is affected. In that way, the damping device acts as a damping valve.
In another embodiment of the invention, a suspension housing, such as in the form of a shock absorber or strut body is utilized to surround the core element. The core element and the case element then form a piston which is movable within the shock absorber or strut body. A suitable piston rod may be coupled to the core element for that purpose. As the piston moves in the shock absorber, and the MR fluid moves past the piston, the magnetic flux in the coils may be selectively controlled to selectively control the damping provided to the piston by the fluid. That is, affecting the fluid flow past the coil element and the case element affects the movement of the piston within the shock absorber. Other uses of the invention in an MR device are also possible.
These features and other features and benefits of the invention are set forth in greater detail below, in the Detailed Description of the invention.